The present invention relates to precision transducers for position measurements and to a method of manufacture thereof. Such position transducers are used in numerically controlled machine tools and in dimension detectors for high-precision machining operations.
In these types of transducers, which generally comprise a pair of supports movable one with respect to the other and each provided with an electric winding constituted by a printed circuit, high precision of the printed circuits and of the supports is necessary. The latter must not deform in the course of time and the short term deformations arising from changes of external variables, such as temperature, humidity, etc., must be known.
Since the parts of the machine to which such transducers are fitted are generally made of cast iron, in order to make the deformations of the supports comparable with those of the parts of the machine, these supports generally consist of steel, aluminum or glass and are separated from the conductor by means of insulation. On a substrate constituted by the support and the insulation, there is disposed a sheet of copper from which the conductors of the winding are formed by photogravure, the conductors thus being extremely precise and perfectly located on the support.
As is known, the winding on one of the two supports of the transducer may be constituted by two groups of conductors, for the sine function and the cosine function respectively, which are intercalated in such manner that intersections of conductors are inevitable, so that it is impossible to produce the winding on a single face, by means of a printed circuit, without other connections. In known circuits, these connections are generally created by soldering auxiliary conductors covered with an insulation to particular platforms or islands and housing these conductors in suitable grooves in the support. The number of these soldered joints is generally high and they make the transducers relatively costly.
Transducers for position measurements have already been proposed in which the winding appertaining to one of the two members is obtained by means of a multi-layer structure. In these transducers, the active conductors of the winding, for example of the slider, are printed partly on one face and partly on the other face of an insulating board. These transducers, however, have the disadvantage that the two parts of the winding are at different distances from the winding of the scale, whereby signals of different intensities are induced, producing errors in the measurements. Moreover, that part of the circuit which is on the face of the board to be bonded to the support undergoes deformation during the bonding operation, which is generally performed after heating under pressure. Finally, it is extremely difficult to obtain acceptable location of the printed circuit when the multi-layer structure is cemented to the support.